The present invention relates generally to an apparatus for producing dry ice from liquid carbon dioxide, and more particularly to a device for automatically regulating or relieving pressure within an interior chamber of a dry ice producing housing.
A well-known method for making dry ice involves dispensing liquid carbon dioxide from a pressurized tank, which is typically held at approximately 800 psi, into a chamber at a pressure below approximately 70 psi, such as at atmospheric pressure. As the liquid carbon dioxide is dispensed, a portion of it changes into carbon dioxide snow through adiabatic expansion and accumulates in the chamber to form a low to medium density block of dry ice, while the remaining portion is directly changed into a gaseous state and released to atmosphere outside the chamber. If desired, the dry ice inside the chamber may then be compacted to form a higher density block.
Once formed, the dry ice can be used in place of ice for cooling substances, keeping substances in a frozen state, carbonating beverages, and so on. With time and the absorption of heat, the dry ice sublimates and returns to its normal gaseous state. Because the dry ice absorbs large quantities of heat during the sublimation process, the rate of sublimation for dry ice is dependent upon its relative compactness, the ambient temperature and pressure surrounding the dry ice, as well as the available surface area for heat absorption.
A small, manually operated dry ice generating device is disclosed in U.S. Pat. No. 4,374,658 to Kawaguchi. This device includes a pressurized source of liquid carbon dioxide and a molding box that accumulates frozen carbon dioxide from a liquid carbon dioxide tank through a nozzle. When assembled, the molding box includes a base, four side walls secured to the base, and a top cover that is securely locked to the side walls through interlocking latches. The side walls of the molding box include a layer of filter material and a plurality of openings to allow the escape of gaseous carbon dioxide during dry ice formation.
Although this type of construction offers some measure of portability and convenience, overpressurization of the molding box with its attendant consequences does pose a concern. Theoretically, the internal pressure of the molding box could reach the internal pressure of the liquid carbon dioxide tank. Excessive pressure within the molding box can be caused by impeded gas flow through the filters when excessive formation and compaction of carbon dioxide snow on the filters occurs. Also, any moisture present on or in the filter or within the molding box due to cleaning or a humid environment could be converted into ice and thus impede the flow of gas. Moreover, if the valve of the pressurized tank is opened fully, an excessive amount of carbon dioxide gas could flow into the molding box and be unable to escape. The primary safety release valve could also become clogged or iced over.
In addition, without the benefit of seeing through the box and into the molding chamber, it may be difficult to ascertain when the dry ice block has reached an acceptable size as well as any problems that may occur during the formation process. Also, during and after formation of the dry ice block, injury may occur when the operator comes into direct contact with the molding box, especially when constructed of a thermally conductive material, since frozen carbon dioxide may be as low as −109° F. Accordingly, prior art molding boxes may include an insulating layer to protect the operator against injury caused by extremely low temperatures.